Fluidic control systems

ABSTRACT

A gas turbine has a fluidic control system having a fluidic bistable element which controls a switch actuator. The vent of the bistable element is fed to a venturi tube. The throat of the venturi tube is connected to one control inlet of the bistable element, the venturi being vented to a pressure equal to or less than the pressure applied to the inlet of the bistable element. The control system is operative to trigger the actuator which in turn controls the gas turbine when the ratio of main inlet pressure of the bistable element to the pressure at the second control inlet falls below a predetermined value; the pressures being respectively taken from the high pressure compression stage and the fan stage of the gas turbine compressor.

United States Paten Davies 1 Aug. 8, 1972 [54] FLUIDIC CONTROL'SYSTEMS [72] Inventor: Guy E. Davies, Fareham,England [73] Assignee: The Plessey Company Limited, Es-

, sex, England [22] Filed: Aug. 20, 1970 [21] Appl. No.: 65,409

30 Foreign Application Priority Data Aug. 23, 1969 Great Britain .42,1'l7/69' [52] U.S.Cl ..137/81.5 [51] Int. Cl ..F15c 1/14, Fl5c 1110 [58] Fieldof Search ..l37/8l.5

[56] References Cited UNITED STATES PATENTS 3,468,326 9/1969 Cohen ..l37/8l.5

3,552,415 l/197lv Small; ..l37/8l.5 3,392,739 7/1968 Taplin etal ..l37/8l.5 3,335,737 8/1967 Gesell ..l37/8l.5

3,232,095 2/l 966 Symnoskiet al......l37/8l.5X

3,572,357 3/197l Philbrick ..l37/8l.5

Primary Examiner-William R. Cline Attorney-Mason, Mason & Albright 57 ABSTRACT.

A gas turbine has a fluidic control system having a fluidic bistable element which controls a switch actuator. The vent of the bistable element is fed to a venturi tube. The throat of the venturi tube is connected to one control inlet of the bistable element, the venturi being vented to a pressure equal to or less than the pressure applied to the inlet of the bistable element.

6 Claim, 4 Drawing Figures Patented Aug. 8, 1972 3 Sheets-Sheet 1 INVENTOR GUY Eownno bAwF-S ATT RNEYS Patented Aug. 8, 1972 3,682,192

- r 3 Sheets-Sheet 2 INVENTOR GUY Eawmzo Mm:

ATTORNEYS Patented Aug. 8, 1972 3,682,192

3 Sheets-Sheet 5 3 PS/PF INVENTOR Guv Eowmab Dames.

v WJJYWWKW TORNEYJ FLUIDIC CONTROL SYSTEMS The present invention relates to fluidic control systems.

The present invention provides a fluidic control system comprising a fluidic actuator, a fluidic'element having an inlet for receiving a first fluid pressure and two control inlets for respectively receiving second and third fluid pressures, said fluidic element being responsive to the pressure difi'erence at the two control inlets to control the fluidic actuator in dependence thereon, and a venturi tube supplying said second fluid pressure from its throat, said venturi tube being connected to receive fluid having a pressure which is substantially proportional to said first fluid pressure whereby to cause the fluidic actuator to operate when the ratio of the first to the third fluid pressures reaches a predetermined value.

According to the invention, there is also provided a gas turbine including an inlet fan stage and-a high pressure compressor stage, a bistable fluidic element having a supply inlet and first and second control inlets and two output legs and an exhaust vent, the supply inlet being connected to receive pressure from said high pressure compressor stage and the first control inlet being arranged to receive pressure from said fan stage, a venturi tube connected to receive pressure from said exhaust vent and having a throat which communicates pressure to said second control inlet, and an actuator, said actuator being responsive to the pressure differential supplied from said output legs to modify the operation of said gas turbine whenever the ratio of the pressures at said fan stage and the compressor stage reaches a predetermined value.

A fluidic control system embodying the invention will now be described by way of example with in FIG. 1) by a pressure P02, and, when fluid is directed down the leg 22, the actuator piston 25 is urged to the right by a pressure P01. The actuator 24 is arranged to operate a microswitch 26.

The adjuster 10 comprises a base plate having an inlet and an outlet hole, an adjustable plate having a plurality of pairs of orifices of different sizes, and a clampplate. All the pairs of'holes in the adjustable plate are linked by an annulus formed in the clamp plate so that, by rotating the adjustable plate, a different pair of holes can be placed in communication with the inlet and outlet of the base plate and the pressure drop across the adjuster altered accordingly.

In operation, fluid at the pressure P., is applied to the pressure ratio setting adjuster 10 which is adjusted to provide the required value of pressure P; at the input 8 of the fluidic element 6. If the pressure ratio P4/PF is relatively low, the vent pressure PV will alsobe relatively low. As the venturi 18 is vented to a pressure equal to or less than PF, the pressure PR at the throat of the venturi 18 will, by virtue of the suction effect produced at the throat, be less than the pressure PF.

Hence fluid from the source of pressure P, will be directed down the leg 20 and thereby cause the actuator 24 to hold the switch 26 in an OFF condition; If the pressure P., then increases relative to the pressure PF, the throat pressure PR will decrease still further until the fluid passing through the throat reaches the speed reference to the accompanying diagrammatic drawings The fluidic control system of FIG. 1 is primarily inf tended to monitor the ratio of the pressure P, in the high pressure stage 7, and the pressure PF in the fan stage 9, inside the compressor of 1 1.

As shown in FIG. 1, a bistable fluidic element 6 has an input 8 which is connected to receive the pressure P, through a pressure ratio setting adjuster 10. The adjuster 10 causes a drop in the pressure P., so that the actual pressure at the input 8 is Pflhe element 6 has two control jet inputs l2 and 14, one of which (12) is connected to receive the pressure PF.

The vent 16 of the bistable element is fed into a venturi tube 18, and the throat of the venturi tube 18 is connected to the other control jet input 14. The venturi is vented to a pressure equal to or less than PF.

The bistable element 6 also hastwo output legs 20 and 22 which are connectedto drive the piston 25 of an actuator 24. Thus, when fluid is directed down the leg 20, the actuator piston 25 is urged to the left (as viewed a gas turbine engine of sound and the venturi becomes choked. Thereafter a further increase in the pressure P, will cause the throat pressure PR to rise until it eventually exceeds the pressure PF. At this moment, the fluid passing down the leg 20 is redirected down the leg 22 which then causes the actuator to operate the switch 26.

In this way the switch 26 is operated to indicate that a predetermined value of the ratio P /PF has been reached.

If the pressure P, now drops so that the pressure PR is below the pressure PF the fluid flow through the bistable element 6 will be redirected down the leg 20. However the value of P /PF at which this occurs will be slightly lower than the value of P /PF at which the original switching occurred because of a hysteresis lag. The electric switch 26 is arranged to control the fuel system of the gas turbine and thereby maintains the pressure ratio P /PF either below or above the predetermined value as required.

Instead the electric switch can be used to control an air valve 13 or other movingpart in the gas turbine.

FIG. 4 shows a graph of the characteristics of the fluidic control system. Curve, A shows the ratio of the sure PF versus the pressure ratio PS/PF. Curve B shows the ratio of differential output pressure POI-P02 versus the control pressure PF. The curves show the initial decrease in pressure due to the suction in the venturi throat, the subsequent increase in pressure as the venturi chokes followed by the switching of the bistable element, and clearly indicates the hysteresis effect.

FIG. 2 shows a modified form of the fluidic control system in which parts similar to those in FIG. 1 are similarly referenced. In this Figure, the venturi tube 18 is not supplied from the vent 16 but instead is supplied direct from the source of pressure P, via a pressure ratio settingadjuster 30.

reached.

3 'With.this system more fluid pressure is available for operating the actuator (not shown) as the adjuster is no longer in the supply path between the source of pressure P, and the fluidic element.

However itwill be seen that because of this the total fluid consumption of the system is increased.

FIG. 3 shows a system in which a fluidic control I system is provided to give an output proportional to the deviation of the pressure ratio PJPF froma PICdt6f7 mined value. Here a proportional amplifier 32 is used instead of a bistable element. As inthe case of FIG. 2,

one control jet input 38 is supplied with pressure P through a variable orifice 36fand a venturi tube 34 while the other control jet'input 40 is supplied with the pressure PF. Two output legs 42 and 44 of the proportional amplifier control a ram 46 in dependence upon pressure difference between the two input control jets. The exhaust vent of the proportional amplifier 32 is providedwith a vent restrictor 48 to increase the effi ciency of the amplifiers 32. v

The ram 46 is coupled to the variable orifice 36 so that if the inlet pressure ratio PJPF increases above a datum value in operation,the ram is caused to be displaced in such a sense as to vary the inlet restrictor to. reduce the ratio PJPF towards its datum value. The of PJPF is ram is then halted when the datum value tuator, said first pressure inlet, control inlets and first and second outlets being connected to interaction chamber means forproducing outlet pressures at said first and outlets respon-J sive to the pressure difi'erence 'at the two control inlets to control the fluidic actuator in dependence thereon, a venturi tube havingan inlet and throat,

first means connecting theinlet of the venturi tube to I receive a fluid presure derived from and proportional to said first fluid pressure, and

two control inlets of .the fluidic element to communicate the second fluid presure to the said one inlet and means for communicating the third fluid pressure to'the other control inlet in anopposing sense whereby to cause the fluidic actuator to operate when the ratio of the first to the third fluid pressures reaches a predetermined value. v

I 2. A system according to claim 1 wherein said fluidicv element has an exhaust vent and in which the first means directly couples theexhaust vent to the venturitube inlet.

3. A system according to claim 1 whereinthe first means comprises a variable orifice through which the first fluid pressureis communicated to-said venturi tube nl t. l A system according to claim 1 wherein the fluidic element comprises. a bistable fluidic element which controls the. operation of mode. u

' 5. A system according to claim I wherein the fluidic element comprises a proportional fluidic amplifier which controls the operation of the actuator in proporthe actuator in an ON/OFF tion to the difference between said second and third pressures.

6. A system according to claim 5 including a variable fluid restrictor connected to the inlet of said fluidic element and means connecting the actuator to the variable fluid restrictor to vary the magnitude of the firstpressure applied to the inlet of the fluidic element in a sense to maintain the ratio of said first to said third pressure constant.

- t t II t second means connecting-the throat to one of said 

1. A fluidic control system comprising a fluidic actuator having first and second inlets, a fluidic element having an inlet for receiving a first fluid pressure, two control inlets for respectively receiving second and third fluid pressures and first and second outlets which are respectively connected to the first and second inlets of the fluid actuator, said first pressure inlet, control inlets and first and second outlets being connected to interaction chamber means for producing outlet pressures at said first and second outlets responsive to the pressure difference at the two control inlets to control the fluidic actuator in dependence thereon, a venturi tube having an inlet and throat, first means connecting the inlet of the venturi tube to receive a fluid pressure derived from and proportional to said first fluid pressure, and second means connecting the throat to one of said two control inlets of the fluidic element to communicate the second fluid pressure to the said one inlet and means for communicating the third fluid pressure to the other control inlet in an opposing sense whereby to cause the fluidic actuator to operate when the ratio of the first to the third fluid pressures reaches a predetermined value.
 2. A system according to claim 1 wherein said fluidic element has an exhaust vent and in which the first means directly couples the exhaust vent to the venturi tube inlet.
 3. A system according to claim 1 wherein the first means comprises a variable orifice through which the first fluid pressure is communicated to said venturi tube inlet.
 4. A system according to claim 1 wherein the fluidic element comprises a bistable fluidic element which controls the operation of the actuator in an ON/OFF mode.
 5. A system according to claim 1 wherein the fluidic element comprises a proportional fluidic amplifier which controls the operation of the actuator in proportion to the difference between said second and third pressures.
 6. A system according to claim 5 including a variable fluid restrictor connected to the inlet of said fluidic element and means connecting the actuator to the variable fluid restrictor to vary the magnitude of the first pressure applied to the inlet of tHe fluidic element in a sense to maintain the ratio of said first to said third pressure constant. 